Let There be Heat!

The Problem. The delivery trip of Shoal Survivor, from Deltaville, VA to Deale, MD took place between Christmas and New Year's (2008-2009); while it was actually quite comfortable at the helm during the day, protected behind the windscreen, it was decidedly chilly watching movies at night, and my daughter and I vowed that we would install heat before the first frost visited us in the next winter.  

The Solution. I belabored the different types of heaters at length. We already had propane, and a spare propane tap existed. The boat was equipped with propane leak detectors and a solenoid valve, further simplifying the decision.  I had a fair idea of the BTU requirement, having spent a few nights on the boat last winter when the temperature dropped into the 20s. I learned that a single 1500 watt space heater didn't quite do it at all and two were just about right. I learned that a vented heater was an absolute requirement, as even cooking with propane in a sealed cabin brought on a slight headache; I'm not certain whether it was lack of oxygen or carbon monoxide.  Applying an appropriate conversion factor (about 3.3 BTUs/watt) and estimating the thermal efficiency at 85%),  5,800 BTUs seem to be the minimum requirement, and perhaps 10,000 BTUs would serve better. The Sig Marine / Dixon P-9000 (5500-7500 BTU output) seemed a reasonable choice and was also the most we really have room for.  A 10 pound bottle of propane should last 50-70 hours, depending on the rate, or most of a season for a $12 refill.

  I  taped a cardboard of the approximate sized to the wall and we lived with it all summer to prove that it was not in the way.



Note on photo: there is a short gap above the heater, between the heater and the air intake pipe. Installation was not finished yet and this was later sealed with a metal band.

Our Experience.

Note 2-19-2010. Winter experience has proven the above numbers. We burned through 20 pounds in 14 very cold December - February days and nights on the boat. I except when on the hook, I have turned the gas off at night and used dock power to run a single 1500 watt space heater. On one very windy 22F night I had to run the heater on low and 2 x 1500 watt heaters in order to keep the entire boat over 70F. I turned the gas off to sleep.

Note 3-24-2013. 3-day cold weather trip (27F-46F). Heater ran most of the time (sometimes on low), plus cooking, and burned about 2-3 pounds each 24 hours. It was off when we left the boat, generally for about 3-6 hours per day.


Installation. While not overly difficult, gas always require meticulous attention to detail. There are Reasoner that on dry land, most jurisdictions no longer allow gas repair and installation parts to be sold to unlicensed individuals. Please be careful, and read-up on the code.

• The gas line must run through a vapor-tight fitting from the propane locker into the cabin. This is a standard item through West Marine, Defender Marine, or Sig / Dickson. The hose is typically pre-assembled with 3/8" flare fittings on each end, so it is a bit fat. The vapor-tight fitting will accommodate this.
• 12 volt electric is required for the fan.  The unit will run without it, but the heat output will be somewhat less and it will not be as well distributed. This is another reason we chose this over the Cozy Cabin Heater. The shut-off safety is not dependent on electricity.
• Installation side clearances are actually quite small for this unit, because the fan circulates cold air around the firebox.  Additionally, the combustion air is drawn through the deck, and around the flu via a double wall pipe. Thus, smokestack never really gets hot on the outside.  The required clearance around the firebox is only 2 inches, and a little bit more around the smokestack. The smoke stack is almost cool enough to hold in your hand by the time it reaches the deck, so no special insulation is needed. The back of the stove and surfaces only a few inches away stay quite cool and no discernible heat is transferred to the bulkhead.
• Mounting. I suppose I could have simply placed screws in the wall, but it's rather heavy and I decided through bolting made more sense.  The backside ( visible inside the head) fold heads are covered with decorative caps matching those used throughout the boat, and I used acorn nuts and on the heater side of the bolts. The holes were over-drilled, filled with epoxy, and re-drilled. ahead is a shower compartment as well and thus is quite wet.  The bulkhead is foam cored.
• Through-deck hole for the smokestack. This was the most stressful step, I assure you.  Boring a 3 1/2-inch, gaping hole through the deck and through the salon roof and extremely visible place - not relaxing at all the first time you commit this sort of surgery on the new boat. It went smoothly enough. After drilling the core was removed extending about 1/2-inch back from the edges and the space filled with epoxy thickened with Cabosil (fumed silica) to a peanut butter consistency. The small holes for the mounting screws were also over drilled and, epoxy-filled, and then re-drilled as well. The smokestack comes with a very thick rubber gasket that is not drilled for the mounting screws; the screws drill their own holes through the rubber and make a very tight fit.
• Heat and epoxy. It is perfectly acceptable to use moderate heat to encourage epoxy to cure more quickly in cool weather. However, there are some caveats: Do not apply significant heat before the epoxy reaches a gel state, as it will become very runny; do not heat thick layers until you are certain they will not exotherm and get hot on their own; it is better to warm the substrate than either the epoxy or the curing mixture after it has gelled.
• Passing the electric wires and gas lines through the bulkhead near the heater was quite simple. I purchased an assortment set of rubber grommets from Home Depot; the largest and second largest nested fit the gas line, and the smallest one accommodated the 2 x 16 gauge wires.
• There is a gap in the flue in the picture - that was covered by a collar, not yet installed, that allows for deck movement.Remember that distance between the heater and the roof changes as you go through waves and as people walk on the deck There is also thermal expansion to consider. Provide for some movement.
• I checked for gas leaks with diluted dish washing liquid and a brush. I have added a simple carbon monoxide detector.  

Note: as of 1-13-2010 the CO monitor has never chirped. There is no odor, moisture, or other side effect. Just like my home gas furnace, in miniature.

• The optional stack heat shield seems unnecessary. The stack stays pretty cool (maximum175 F with infrared thermometer - hurts, but would not burn very quickly). Also, the guard will only fit if the stack is straight.

• The deck guard is necessary; the stack (deck cap, included with the heaters and pictured to the left) is a VERY effective sheet grabber and will foul your sheets on every tack. I built a similar custom guard from 1/8" x 3/4" aluminum strap that stands 5" high by 12" across, since the custom guard from Dickson was not streamlined enough to effectively shed sheets.
•  Distributing the heat. We direct a small pre-existing fan (at first a Hella Turbo, now a Camaro Bora), set on low, at the stack and heater, blowing downwards. It increases the heater out-put by cooling the pipe and exterior, and helps spread the heat evenly throughout the cabin, floor to ceiling, without producing an objectionable draft. I'm sure location is critical, so experiment with your geometry.

About five hours of labor, overall.  The only hideous step was drilling the hole into the propane locker.  That involved boat yoga, worming into one of the under seat lockers in the saloon, which is obviously not designed for human habitation.

Although the heater doesn't get hot on the outside, thanks to the fan and jacket configuration, the glass front gets hot enough to take some paint off your hand. My daughter has also determined that with the door open and the flame set on low, it can be used for somores!

I'm now actually looking forward to our first overnight trip in true winter weather. I like winter: in the summer, there is a limit as to how many clothes you can take off; in the winter it is a simple matter to layer up with modern fleece and stretch products, enough to be comfortable in anything. My other joy is ice climbing; watch me enjoying a New Hampshire icefall at ~ -10F... and loving every moment. There is no swimming in the winter. The wind can howl and often does. Beach combing is different. Many Bay area businesses close for the season. But it is still beautiful.

Experience note, 1-13-2010: operation at the dock and underway has been flawless. Spray and moderate wind have caused no ill effects. Wind gusts of 25 knots apparent have caused flame-outs, but the unit interrupted the gas flow quickly. The heat generally stays in the salon, leaving the cabins quite cool, and so thick blankets are required. I like it that way. At dock, we use small electric space heaters on low in the cabins.

Note on thermal efficiency. The exhaust gases go through a double-pipe heat exchanger, giving up heat to the incoming combustion air. The draft is controlled (there is not too much excess air, as the gas flame is yellow) and waste up the stack is reduced (the maximum stack temperature is only about 285 F by IR thermometer). Thus, depending on the assumptions, the of the heater is about 85% efficient , as good as you will find short of a high-efficiency condensing heater, not available for boats. Most marine heaters are 70-80% efficient and have much higher exhaust temperatures.

10-22-2011: I just returned from another cool weather trip; still working well. As it is a vented heater, it warms the boat without humidity increase, CO or CO2 risk, and is without odor. 

3-24-2013: Some continuing problems with flame blowing out if sailing with wind on beam above 20 knots. I need to upgrade the deflector. No problems at anchor, only with wind on beam. 

A simple. dependable solution, without the complications of forced air heat. Not what I would do if I lived aboard, but just fine for the occasional year-round cruiser.

A Lot of Hidden Work

Rev. 7-25-2024

Installing air air conditioning is like a lot of projects; all the hard work is hidden, and if you do it right, it doesn't look like you did anything. I put in a good 20 hours worth on this, not counting head-scratching time. And I work fast.

This has been sold...

Replaced by this.

The short version is that the installation work is considerable, but it is MUCH quieter, easier to use, delivers 50% more BTUs, and consumes 23% fewer amps. Best of all, it does not leak rain, freeze the person sitting under it, snag sheets, or block the helm view. The weight is slightly less and is carried lower.It actually takes a little more space, just hidden in lockers. It can actually run it off the batteries for 4-6 hours once the cabin is cooled down (meaning I can leave a marina in the morning and leave it one until we are out in the breeze). Fortunately, I kept the lockers pretty cleaned out, so I still have far more storage than I need.

Detailed write-up coming to Good Old Boat Magazine. Meanwhile, if you're looking for AC, I've got nothing but good things to say about the folks at Dometic. Great unit and great tech support (I had no trouble with the installation, but I had a lot of tech questions for the article). The toughest part is running the ducts to the optimum positions, which is very important. Not as difficult, but also very important, is plumbing the water intake so that the pipe rises steadily, without loops, through the strainer and through the pump. If there are loops, the system will air lock after hard sailing. Finally, place the temperature sensor in the warm return, out of the cold blast, to avoid short cycling. Don't draw the return air from bilge space; you can pick-up odors, fuel fumes and even CO. Run a separate plenum from the cabin.

And the obvious. Keep the door closed to reduce humidity and icing. Don't expect it to work in water over 90F (check the manual for limitations) and separate the intake and discharge. Reflective window covers and awnings will greatly reduce the work load. Insulate if possible.

Dehumidifier vs Desicant

Four years ago, in the fall I noticed something I had not seen before; the dreaded black spots, this time on cabin carpeting. Clearly, better humidity control was in order for the cooler season.

A large compressor unit would be a beast on a small boat. Though I have a 30-pint unit at home, the downsides are major:

• A lot of amps on the shore power cord.
• A back injury waiting to happen; the unit is huge and awkward.
• In the way.
• Loud.
•  More capacity than I needed.

 
So I looked around and found the Eva-Dry 2200. The no-compressor  principle is elegant, the only moving part being a small fan. The over simplified explanation is that of a thermocouple, but in reverse. Instead of a temperature difference creating a small electric current, the current is forced in the reverse direction through a whole stack of thermocouples, creating a cold plate. Water condenses on the cold plate and runs into a tank.

The size and weight (just a few pounds) are appropriate; when not in use it's easy to swing it into a cabinet for storage, although for day sailing I just put it in the sink to keep it from falling. They are prone to icing in temperatures below about 45F, but deicing by controlling the run cycle with a light timer is simple; 8 hours on at night and 6 hours off during the day. Even in the depths of the winter, the interior of the boat warms above freezing during the day due to solar heating.

I modified the tank by drilling a hole and tapping in a 1/4 NPT x 3/16" ID hose barb. The hose runs to the sink so that it never fills and to prevent freezing and breaking in the winter.

 So far--four years--the unit has just  purred along, removing 2-8 ounces per day, keeping the relative humidity at 45-65% at temperatures from below freezing to 95F. The boat is always dry, the bedding fresh, and interior corrosion issue non-existent.Just like home.
 

 

 Cold plate frosted

Cold Plate Thawed 

The only real alternative is calcium chloride descant. I did an article about these for Practical Sailor  magazine and still had a few left over. I held a race several years ago, the Eva-Dry in the port cabin and a large absorbant bag on starboard. It wasn't even close. It would take ten 5-pound buckets of CaCl2 to do what this unit will do over 3-4 month winter season.

I also tested a cheaper version from Perfect Home. It lasted about 8 months, just like the reviews said it would.

Keeping a Cruise-and-Carry AC unit On-deck: Good Idea, or Dissaster in the Making?

rev. 6-27-2016

Note: this is my experience with a catamaran, with a relatively level deck. If you have a leaner (monohull) your experience could be different. Additionally, our cabin top is high above the water and the ride is generally dry; if you have a chronically wet deck, that would be very different.

Spring 2016 we replaced this with Dometic Turbo installed air conditioning. Expensive, but slightly less weight, much quieter, much more even cold distribution, more BTUs, less amps, clear deck, better visibility, less lugging, and no blocked hatch. Yup, it's better all around. If you can do the installation work yourself, installed is the far better value. However, installed is a little complicated. I have an article scheduled for publication spring 2018. Quite a lead time.

I posted this question on several forums and received the expected doomsayer advice: it will slide off and kill someone; it will slide off and kill someone every time there's rough weather; because it will slide off an kill someone you must figure out some way to get it below every single time you move the boat. Given the narrow side decks of my boat and given the unreliable character of my back, if I had to tote the unit around and down below, if the unit has to go below every day, then I might as well throw it over the side the first morning be done with it.

The reality was not so grim.

I carried our A/C unit on deck for the better part of a 500 mile cruise around the Delmarva Peninsula. I carried it on deck through small craft advisory conditions, close reaching up-wind at 8-9 knots, spray covering the boat. We carried on through rain. We carried on through 8-foot swells generated by hurricane Bill, taking green water the length of the boat on one occasion. With two simple straps through the carrying handles, the unit never shifted an inch. We did get a few drops now and then when there was heavy spray or rain. When we took green water probably a teacup came around the edges. Thankfully, that was one stray breaker; if it had been more than that we've certainly would've taken it below. We get nearly as much leakage from condensate in humid conditions. We learn that a large beach towel laid over the hatch shroud as insulation eliminated the condensation.
The straps are the sheet from the self-tacking jib (we use the 150% genny most of the time) and a length of 5/16-inch low-stretch line tied with a truckers hitch. This was very secure and took only a minute to rig each time.
We also learned that it's a simple matter, at least on the PDQ 32, to lower the unit down through the slider at the far outboard edge, and then forward onto the port saloon bench. It is a one-person job and settled weather and an easy two-person job even when it's little bouncy. Do pad the open vinyl window with a towel to prevent scratching.

Would I keep the unit on deck as much as we did before, knowing what I know now? No. I would take it down anytime 20 knots of wind as predicted or anytime large breaking swells are a likelihood. If a thunderstorm approached I would probably put down the hatch, if I believed that waves would be an issue. It is also a bloody nuisance if frequent tacking is anticipated. But for cruising in fine weather and light rain, were tacks tend to be far apart, yes, next summer it will live on deck.

Tip: If you cover the canvas hatch adapter with a large beach towel, dripping from condensation and leaking during rain storms will be less, and efficiency will be greater. Do not block the cooling fan grating.

Tip: Cut a 24-inch square foam floor tiles to fit the AC unit and opening. This greatly reduces both condensation and rain leaks.

Tip: The existing leveling leg will not maintain its position underway and under the pressure of lashings; the cam will slip. Drill holes, about 9/32- to 11/32-inch or as needed to produce a light push fit, through the leg athwart ships to accommodate a section of FRP tent pole. I also added a layer of EVA foam to the bottom of the foot, for additional padding, after the original rubber moulding fell off.